1. Field of Invention
This invention relates generally to wireless communications. In particular, the invention relates to systems and methods for providing electrical power by a portable unit to a base unit.
2. Background Art
Devices enabling wireless communications are becoming increasingly popular. One example of this trend is cordless telephony. Cordless telephones have largely replaced conventional corded telephones in many homes by providing enhanced features and flexibility in conducting telephonic communications.
Unlike conventional consumer corded telephones, which typically operate solely from power supplied by the public switched telephone network (PSTN), cordless telephones typically require an external power source to enable their operation. Specifically, such telephones are typically supplied with a DC power adapter which must be connected to a wall power outlet. The increased amount of power that can be supplied via the power outlet, compared to the public switched telephone network, enables operation of the base unit transmitter and receiver circuits required for cordless operation, as well as other advanced features such as integrated answering machines and/or base unit speakerphones.
However, the requirement for an external power source can be disadvantageous in the event of a power outage because many cordless telephone systems become inoperable. A power outage may be especially problematic because power outages often occur during emergencies such as severe weather, or other situations during which a person may wish to call for help. Because cordless telephones are so popular, many people do not even own a conventional corded telephone and thus they will be completely unable to make or receive telephone calls in power outage circumstances. Even those who retain an old corded telephone in storage will be forced to find and connect the corded telephone before any calls can be made. Finding and connecting a stored corded telephone may be particularly difficult during a power outage without lights.
Recently, multi-handset cordless telephone systems have become popular among consumers. Such systems typically include a single base unit capable of communicating with multiple cordless handsets, each handset being powered by its own rechargeable battery. Each cordless handset then requires only a charging base to maintain the battery level in the handset. In such systems, handsets can be positioned in any area within the home or office at which a power outlet is available, thereby providing increased flexibility compared to conventional single-handset models that also require a telephone line connection for each handset. Furthermore, the handset charging base is typically substantially smaller and more aesthetically pleasing than a conventional cordless telephone base unit. However, as with conventional cordless telephones, most multi-handset cordless telephone systems are also disabled if the wall outlet power supply to the base unit fails.
One solution to the problems of power outages is to provide a backup battery within the cordless telephone base unit. Such a system is described in U.S. Pat. No. 5,578,875, assigned to VTech Communications, Ltd. When a power outage occurs, the base unit switches its power input from the line input to the backup battery resident in the base unit. Accordingly, the base unit remains operational and available to make and receive telephone calls until the base unit backup battery is depleted.
However, a battery pack is typically a costly component of a cordless telephone system. Providing an extra base unit battery pack with each cordless telephone system adds substantially to the cost of the telephone, placing such a telephone at a competitive disadvantage. While the base unit battery pack can be sold separately, consumers desiring the backup power supply feature are still burdened with the added cost of purchasing the second battery. Moreover, many consumers opt not to incur the substantial cost of a base battery pack due to the perceived rarity of circumstances in which such a battery pack would be required. Such consumers are then severely inconvenienced when their power inevitably does fail.
Therefore, it would be highly desirable to enable operation of a cordless telephone system during a power outage with minimal extra cost. This and other objects of the invention will become apparent in view of the disclosure herein.